High tear films from hafnocene catalyzed polyethylenes

ABSTRACT

A polyethylene film having a balance of improved physical and mechanical properties and a method for making the same are provided. In one aspect, the film includes a 1% secant modulus of greater than 25,000 psi, a dart impact resistance of greater than 500 g/mil, and a MD tear strength of greater than 500 g/mil. In one aspect, the method comprises reacting ethylene derived units and a comonomer in the presence of a hafnium-based metallocene at a temperature of from 70° C. and 90° C., an ethylene partial pressure of from 120 psia and 260 psia, and a comonomer to ethylene ratio of from 0.01 to 0.02 to produce an ethylene based polymer. The method further comprises extruding the ethylene based polymer at conditions sufficient to produce a polyethylene film comprising a secant modulus of greater than 25,000 psi, a dart impact resistance of greater than 500 g/mil, and a MD tear strength of greater than 500 g/mil.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.10/737,654, filed Dec. 15, 2003, which is a continuation-in-part ofco-pending U.S. patent application Ser. No. 10/199,446, filed Jul. 19,2002 which claims benefit of provisional application Ser. No.60/306,600, filed Jul. 19, 2001. Each of the aforementioned relatedpatent applications are herein incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to films that exhibit a superior balanceof physical properties. The films are produced with polyethylenes havinga broad composition distribution (CD) and molecular weight distribution(MWD).

2. Description of the Related Art

Metallocene-catalyzed ethylene polymers are known to produce tough filmsmeasured in terms of dart drop impact strength (dart). ConventionalZiegler-Natta catalyzed linear low density polyethylenes (Z-N LLDPE) areknown to have good processability, stiffness and tear strength, asmeasured by extruder pressures and motor load, 1% secant modulus, andElmendorf tear strength. Ideally, a polyethylene resin would have Z-NLLDPE processability and produce a film exhibiting a combination ofmetallocene like toughness and Ziegler-Natta like stiffness and tearstrength. It is possible to improve the toughness of films (e.g. MDtensile strength) by increasing the amount of orientation in the machinedirection during film blowing. However, conventional knowledge in thepolyethylene film art says that by increasing the machine direction (MD)orientation in films during manufacture of these films, other physicalproperties, such as MD tear strength, will decrease.

To this point, in Polymer Engineering and Science, mid-October 1994,vol. 34, No. 19, the disclosure of which is incorporated herein byreference, the authors discuss processing structure propertiesrelationships in polyethylene blown film. The authors suggest that MDElmendorf tear is found to be inversely related to drawdown ratio and MDshrinkage.

Further, in Polymer, 41 (2000) 9205-9217, the disclosure of which isincorporated herein by reference, the authors suggest that at high MDextension rates, a greater number of molecules will be oriented alongthe MD prior to the onset of crystallization, and that this isdetrimental from a MD tear performance perspective.

Metallocene catalyst components can be combined to form blendcompositions as described in PCT publication WO 90/03414 published Apr.5, 1990, the disclosure of which is incorporated herein by reference.Also mixed metallocenes as described in U.S. Pat. Nos. 4,937,299 and4,935,474, the disclosure of both which are incorporated herein byreference, can be used to produce polymers having a broad molecularweight distribution and/or a multimodal molecular weight distribution.

U.S. Pat. No. 5,514,455 suggests that a reduction in gauge ofpolyethylene films results in an increase in tear values. This documentemploys a titanium magnesium catalyst for polyethylene production andincludes titanium residues in the polyethylene. Reported values ofElmendorf machine direction (MD) tear to transverse direction (TD) tear,are in the range of 0.1-0.3 for inventive examples.

U.S. Pat. No. 5,744,551, the disclosure of which is incorporated hereinby reference, suggests a balance of tear property improvement. Thisdocument also employs a titanium magnesium catalyst for polyethyleneproduction and includes titanium residues in the polyethylene. Further,the MD/TD tear ratios are in the range of 0.63-0.80 for inventiveexamples.

U.S. Pat. No. 5,382,630, the disclosure of which is incorporated hereinby reference, discloses linear ethylene interpolymer blends made fromcomponents that can have the same molecular weight but differentcomonomer contents, or the same comonomer contents but differentmolecular weights, or comonomer contents which increase with molecularweight. U.S. Pat. No. 5,382,630 suggests multimodal polyethylene blendsfor which tear strength can be controlled. However, this document usesonly intrinsic tear, and is silent on Elmendorf MD/TD tear ratios and onany other values but intrinsic tear.

Also, in U.S. Pat. No. 6,242,545 and U.S. Pat. No. 6,248,845 as well asprovisional applications U.S. Ser. No. 60/306,503 filed Jul. 19, 2001and 60/306,903 filed Jul. 19, 2001, the disclosures of all which areincorporated herein by reference, the patentees/applicants of thesedocuments reported production of either broad composition distribution,narrow molecular weight, or broad composition distribution, relativelybroad molecular weight distribution polyethylenes. However, thesedocuments show an improvement in cast film MD tear, but no appreciableimprovement for blown film.

There is a need, therefore, for a polyolefin film, more specifically ablown polyethylene film, that has high machine direction tear (MD tear)and/or high transverse direction tear (TD tear), and/or high dart dropimpact resistance (dart), made from a polyethylene that is easier toprocess than prior metallocene catalyst produced linear low densitypolyethylenes (mLLDPE). In other words it is desirable to have theprocessability, stiffness and tear strength of a ZN-LLDPE combined withthe dart impact strength of a mLLDPE.

SUMMARY OF THE INVENTION

A polyethylene film having a balance of improved physical and mechanicalproperties and a method for making the same are provided. In one aspect,the film includes a 1% secant modulus of greater than 25,000 psi, a dartimpact resistance of greater than 500 g/mil, and a MD tear strength ofgreater than 500 g/mil. In another aspect, the film comprises anethylene based polymer produced in the presence of a hafnium-basedmetallocene within a gas phase reactor operated at a temperature of from70° C. and 90° C. and at an ethylene partial pressure of from 120 psiaand 260 psia.

In yet another aspect, a film is provided by extruding an ethylene basedpolymer produced in the presence of a hafnium-based metallocene within agas phase reactor operated at a temperature of from 70° C. and 90° C.and at an ethylene partial pressure of from 120 psia and 260 psia,wherein the film comprises a 1% secant modulus of greater than 25,000psi, a dart impact resistance of greater than 500 g/mil, and a MD tearstrength of greater than 500 g/mil.

The method for producing a film having a balance of improved physicaland mechanical properties comprises reacting ethylene derived units anda comonomer in the presence of a hafnium-based metallocene at atemperature of from 70° C. and 90° C., an ethylene partial pressure offrom 120 psia and 260 psia, and a comonomer to ethylene ratio of from0.01 to 0.02 to produce an ethylene based polymer. The method furthercomprises extruding the ethylene based polymer at conditions sufficientto produce a polyethylene film comprising a 1% secant modulus of greaterthan 25,000 psi, a dart impact resistance of greater than 500 g/mil, anda MD tear strength of greater than 500 g/mil.

DETAILED DESCRIPTION

Films having a unique balance of machine direction (MD) and transversedirection (TD) tear, and/or a simultaneously increasing MD tear withincreasing MD shrinkage are provided. It has been surprisingly foundthat these improved properties are a result of a polymer having a broadcomonomer distribution (CD) and molecular weight distribution (MWD).Further, it has been surprisingly found that the comonomer distributionand molecular weight distribution of the polymer are produced bycontrolling either the reactor temperature or ethylene partial pressureor both in the presence of a hafnium-based metallocene catalyst(“metallocene” or “hafnocene”) or hafnocene catalyst system.

A “catalyst system” as used herein may include one or morepolymerization catalysts, activators, supports/carriers, or anycombination thereof, and the terms “catalyst” and “catalyst system” areintended to be used interchangeably herein. The term “supported” as usedherein refers to one or more compounds that are deposited on, contactedwith, vaporized with, bonded to, or incorporated within, adsorbed orabsorbed in, or on, a support or carrier. The terms “support” or“carrier” for purposes of this specification are used interchangeablyand are any support material, preferably a porous support material,including inorganic or organic support materials. Non-limiting examplesof inorganic support materials include inorganic oxides and inorganicchlorides. Other carriers include resinous support materials such aspolystyrene, functionalized or crosslinked organic supports, such aspolystyrene, divinyl benzene, polyolefins, or polymeric compounds,zeolites, talc, clays, or any other organic or inorganic supportmaterial and the like, or mixtures thereof.

Catalyst Components and Catalyst Systems

Hafnocenes are generally described throughout in, for example, 1 & 2METALLOCENE-BASED POLYOLEFINS (John Scheirs & W. Kaminsky eds., JohnWiley & Sons, Ltd. 2000); G. G. Hlatky in 181 COORDINATION CHEM. REV.243-296 (1999) and in particular, for use in the synthesis ofpolyethylene in 1 METALLOCENE-BASED POLYOLEFINS 261-377 (2000). Thehafnocene compounds as described herein include “half sandwich” and“full sandwich” compounds having one or more Cp ligands(cyclopentadienyl and ligands isolobal to cyclopentadienyl) bound to ahafnium atom, and one or more leaving group(s) bound to the hafniumatom. Hereinafter, these compounds will be referred to as “hafnocences,”“metallocenes,” or “metallocene catalyst components”. The hafnocene maybe supported on a support material in a particular embodiment asdescribed further below, and may be supported with or without anothercatalyst component or components.

As used herein, in reference to Periodic Table “Groups” of Elements, the“new” numbering scheme for the Periodic Table Groups are used as in theCRC HANDBOOK OF CHEMISTRY AND PHYSICS (David R. Lide ed., CRC Press81^(st) ed. 2000).

The Cp ligands are one or more rings or ring system(s), at least aportion of which includes π-bonded systems, such as cycloalkadienylligands and heterocyclic analogues. The ring(s) or ring system(s)typically comprise atoms selected from the group consisting of Groups 13to 16 atoms, and more particularly, the atoms that make up the Cpligands are selected from the group consisting of carbon, nitrogen,oxygen, silicon, sulfur, phosphorous, germanium, boron and aluminum andcombinations thereof, wherein carbon makes up at least 50% of the ringmembers. Even more particularly, the Cp ligand(s) are selected from thegroup consisting of substituted and unsubstituted cyclopentadienylligands and ligands isolobal to cyclopentadienyl, non-limiting examplesof which include cyclopentadienyl, indenyl, fluorenyl and otherstructures. Further non-limiting examples of such ligands includecyclopentadienyl, cyclopentaphenanthreneyl, indenyl, benzindenyl,fluorenyl, octahydrofluorenyl, cyclooctatetraenyl,cyclopentacyclododecene, phenanthrindenyl, 3,4-benzofluorenyl,9-phenylfluorenyl, 8-H-cyclopent[a]acenaphthylenyl, 7H-dibenzofluorenyl,indeno [1,2-9]anthrene, thiophenoindenyl, thiophenofluorenyl,hydrogenated versions thereof (e.g., 4,5,6,7-tetrahydroindenyl, or“H₄Ind”), substituted versions thereof (as described in more detailbelow), and heterocyclic versions thereof.

In one aspect of the invention, the one or more metallocene catalystcomponents of the invention are represented by the formula (I):Cp^(A)Cp^(B)HfX_(n)  (I)

-   -   wherein each X is chemically bonded to Hf; each Cp group is        chemically bonded to Hf; and n is 0 or an integer from 1 to 4,        and either 1 or 2 in a particular embodiment.

The ligands represented by Cp^(A) and Cp^(B) in formula (I) may be thesame or different cyclopentadienyl ligands or ligands isolobal tocyclopentadienyl, either or both of which may contain heteroatoms andeither or both of which may be substituted by a group R. In oneembodiment, Cp^(A) and Cp^(B) are independently selected from the groupconsisting of cyclopentadienyl, indenyl, tetrahydroindenyl, fluorenyl,and substituted derivatives of each.

Independently, each Cp^(A) and Cp^(B) of formula (I) may beunsubstituted or substituted with any one or combination of substituentgroups R. Non-limiting examples of substituent groups R as used instructure (I) include hydrogen radicals, alkyls, alkenyls, alkynyls,cycloalkyls, aryls, acyls, aroyls, alkoxys, aryloxys, alkylthiols,dialkylamines, alkylamidos, alkoxycarbonyls, aryloxycarbonyls,carbomoyls, alkyl- and dialkyl-carbamoyls, acyloxys, acylaminos,aroylaminos, and combinations thereof.

More particular non-limiting examples of alkyl substituents R associatedwith formula (I) through (V) include methyl, ethyl, propyl, butyl,pentyl, hexyl, cyclopentyl, cyclohexyl, benzyl, phenyl, methylphenyl,and tert-butylphenyl groups and the like, including all their isomers,for example tertiary-butyl, isopropyl, and the like. Other possibleradicals include substituted alkyls and aryls such as, for example,fluoromethyl, fluroethyl, difluroethyl, iodopropyl, bromohexyl,chlorobenzyl and hydrocarbyl substituted organometalloid radicalsincluding trimethylsilyl, trimethylgermyl, methyldiethylsilyl and thelike; and halocarbyl-substituted organometalloid radicals includingtris(trifluoromethyl)silyl, methylbis(difluoromethyl)silyl,bromomethyldimethylgermyl and the like; and disubstituted boron radicalsincluding dimethylboron for example; and disubstituted Group 15 radicalsincluding dimethylamine, dimethylphosphine, diphenylamine,methylphenylphosphine, Group 16 radicals including methoxy, ethoxy,propoxy, phenoxy, methylsulfide and ethylsulfide. Other substituents Rinclude olefins such as but not limited to olefinically unsaturatedsubstituents including vinyl-terminated ligands, for example 3-butenyl,2-propenyl, 5-hexenyl and the like. In one embodiment, at least two Rgroups, two adjacent R groups in one embodiment, are joined to form aring structure having from 3 to 30 atoms selected from the groupconsisting of carbon, nitrogen, oxygen, phosphorous, silicon, germanium,aluminum, boron and combinations thereof. Also, a substituent group Rgroup such as 1-butanyl may form a bonding association to the hafniumatom.

Each X in the formula (I) above and for the formulas/structures (II)through (V) below is independently selected from the group consistingof: any leaving group in one embodiment; halogen ions, hydrides, C₁ toC₁₂ alkyls, C₂ to C₁₂ alkenyls, C₆ to C₁₂ aryls, C₇ to C₂₀ alkylaryls,C₁ to C₁₂ alkoxys, C₆ to C₁₆ aryloxys, C₇ to C₁₈ alkylaryloxys, C₁ toC₁₂ fluoroalkyls, C₆ to C₁₂ fluoroaryls, and C, to C₁₂heteroatom-containing hydrocarbons and substituted derivatives thereofin a more particular embodiment; hydride, halogen ions, C₁ to C₆ alkyls,C₂ to C₆ alkenyls, C₇ to C₁₈ alkylaryls, C₁ to C₆ alkoxys, C₆ to C₁₄aryloxys, C₇ to C₁₆ alkylaryloxys, C₁ to C₆ alkylcarboxylates, C₁ to C₆fluorinated alkylcarboxylates, C₆ to C₁₂ arylcarboxylates, C₇ to C₁₈alkylarylcarboxylates, C₁ to C₆ fluoroalkyls, C₂ to C₆ fluoroalkenyls,and C₇ to C₁₈ fluoroalkylaryls in yet a more particular embodiment;hydride, chloride, fluoride, methyl, phenyl, phenoxy, benzoxy, tosyl,fluoromethyls and fluorophenyls in yet a more particular embodiment; C₁to C₁₂ alkyls, C₂ to C₁₂ alkenyls, C₆ to C₁₂ aryls, C₇ to C₂₀alkylaryls, substituted C₁ to C₁₂ alkyls, substituted C₆ to C₁₂ aryls,substituted C₇ to C₂₀ alkylaryls and C₁ to C₁₂ heteroatom-containingalkyls, C₁ to C₁₂ heteroatom-containing aryls and C₁ to C₁₂heteroatom-containing alkylaryls in yet a more particular embodiment;chloride, fluoride, C₁ to C₆ alkyls, C₂ to C₆ alkenyls, C₇ to C₁₈alkylaryls, halogenated C₁ to C₆ alkyls, halogenated C₂ to C₆ alkenyls,and halogenated C₇ to C₁₈ alkylaryls in yet a more particularembodiment; fluoride, methyl, ethyl, propyl, phenyl, methylphenyl,dimethylphenyl, trimethylphenyl, fluoromethyls (mono-, di- andtrifluoromethyls) and fluorophenyls (mono-, di-, tri-, tetra- andpentafluorophenyls) in yet a more particular embodiment.

Other non-limiting examples of X groups in formula (I) include amines,phosphines, ethers, carboxylates, dienes, hydrocarbon radicals havingfrom 1 to 20 carbon atoms, fluorinated hydrocarbon radicals (e.g., —C₆F₅(pentafluorophenyl)), fluorinated alkylcarboxylates (e.g., CF₃C(O)O⁻),hydrides and halogen ions and combinations thereof. Other examples of Xligands include alkyl groups such as cyclobutyl, cyclohexyl, methyl,heptyl, tolyl, trifluoromethyl, tetramethylene, pentamethylene,methylidene, methyoxy, ethyoxy, propoxy, phenoxy, bis(N-methylanilide),dimethylamide, dimethylphosphide radicals and the like. In oneembodiment, two or more X's form a part of a fused ring or ring system.

In another aspect, the metallocene catalyst component includes those offormula (I) where Cp^(A) and Cp^(B) are bridged to each other by atleast one bridging group, (A), such that the structure is represented byformula (II):Cp^(A)(A)Cp^(B)HfX_(n)  (II)

These bridged compounds represented by formula (II) are known as“bridged metallocenes”. Cp^(A), Cp^(B), X and n in structure (II) are asdefined above for formula (I); and wherein each Cp ligand is chemicallybonded to Hf, and (A) is chemically bonded to each Cp. Non-limitingexamples of bridging group (A) include divalent hydrocarbon groupscontaining at least one Group 13 to 16 atom, such as but not limited toat least one of a carbon, oxygen, nitrogen, silicon, aluminum, boron,germanium and tin atom and combinations thereof; wherein the heteroatommay also be C₁ to C₁₂ alkyl or aryl substituted to satisfy neutralvalency. The bridging group (A) may also contain substituent groups R asdefined above (for formula (I)) including halogen radicals and iron.More particular non-limiting examples of bridging group (A) arerepresented by C₁ to C₆ alkylenes, substituted C₁ to C₆ alkylenes,oxygen, sulfur, R′₂C═, R′₂Si═, —Si(R′)₂Si(R′₂)═, R′₂Ge═, R′P═(wherein“═” represents two chemical bonds), where R′ is independently selectedfrom the group consisting of hydride, hydrocarbyl, substitutedhydrocarbyl, halocarbyl, substituted halocarbyl, hydrocarbyl-substitutedorganometalloid, halocarbyl-substituted organometalloid, disubstitutedboron, disubstituted Group 15 atoms, substituted Group 16 atoms, andhalogen radical; and wherein two or more R′ may be joined to form a ringor ring system. In one embodiment, the bridged metallocene catalystcomponent of formula (II) has two or more bridging groups (A).

Other non-limiting examples of bridging group (A) include methylene,ethylene, ethylidene, propylidene, isopropylidene, diphenylmethylene,1,2-dimethylethylene, 1,2-diphenylethylene, 1,1,2,2-tetramethylethylene,dimethylsilyl, diethylsilyl, methyl-ethylsilyl,trifluoromethylbutylsilyl, bis(trifluoromethyl)silyl, di(n-butyl)silyl,di(n-propyl)silyl, di(i-propyl)silyl, di(n-hexyl)silyl,dicyclohexylsilyl, diphenylsilyl, cyclohexylphenylsilyl,t-butylcyclohexylsilyl, di(t-butylphenyl)silyl, di(p-tolyl)silyl and thecorresponding moieties wherein the Si atom is replaced by a Ge or a Catom; dimethylsilyl, diethylsilyl, dimethylgermyl and diethylgermyl.

In another embodiment, bridging group (A) may also be cyclic,comprising, for example 4 to 10, 5 to 7 ring members in a moreparticular embodiment. The ring members may be selected from theelements mentioned above, from one or more of B, C, Si, Ge, N and O in aparticular embodiment. Non-limiting examples of ring structures whichmay be present as or part of the bridging moiety are cyclobutylidene,cyclopentylidene, cyclohexylidene, cycloheptylidene, cyclooctylidene andthe corresponding rings where one or two carbon atoms are replaced by atleast one of Si, Ge, N and O, in particular, Si and Ge. The bondingarrangement between the ring and the Cp groups may be either cis-,trans-, or a combination.

The cyclic bridging groups (A) may be saturated or unsaturated and/orcarry one or more substituents and/or be fused to one or more other ringstructures. If present, the one or more substituents are selected fromthe group consisting of hydrocarbyl (e.g., alkyl such as methyl) andhalogen (e.g., F, Cl) in one embodiment. The one or more Cp groups whichthe above cyclic bridging moieties may optionally be fused to may besaturated or unsaturated and are selected from the group consisting ofthose having 4 to 10, more particularly 5, 6 or 7 ring members (selectedfrom the group consisting of C, N, O and S in a particular embodiment)such as, for example, cyclopentyl, cyclohexyl and phenyl. Moreover,these ring structures may themselves be fused such as, for example, inthe case of a naphthyl group. Moreover, these (optionally fused) ringstructures may carry one or more substituents. Illustrative,non-limiting examples of these substituents are hydrocarbyl(particularly alkyl) groups and halogen atoms.

The ligands Cp^(A) and Cp^(B) of formula (I) and (II) are different fromeach other in one embodiment, and the same in another embodiment.

Some specific, non-limiting examples of hafnocenes include bis(n-propylcyclopentadienyl) hafnium dichloride, bis(n-propyl cyclopentadienyl)hafnium difluoride, bis(n-propyl cyclopentadienyl) hafnium dimethyl,bis(n-propyl cyclopentadienyl) hafnium dihydride,bis(2-propenylcyclopentadienyl) hafnium dichloride,bis(2-propenylcyclopentadienyl) hafnium difluoride,bis(2-propenylcyclopentadienyl) hafnium dimethyl, bis(n-butylcyclopentadienyl) hafnium dichloride, bis(n-butyl cyclopentadienyl)hafnium difluoride, bis(n-butyl cyclopentadienyl) hafnium dimethyl,bis(3-butenylcyclopentadienyl) hafnium dichloride,bis(3-butenylcyclopentadienyl) hafnium difluoride,bis(3-butenylcyclopentadienyl) hafnium dimethyl, bis(n-pentylcyclopentadienyl) hafnium dichloride, bis(n-pentyl cyclopentadienyl)hafnium difluoride, bis(n-pentyl cyclopentadienyl) hafnium dimethyl,(n-propyl cyclopentadienyl)(n-butyl cyclopentadienyl) hafnium dichlorideor dimethyl, bis(trimethylsilylmethylcyclopentadienyl) hafniumdichloride, bis[(2-trimethylsilyl-ethyl)cyclopentadienyl]hafniumdichloride or dimethyl, bis(trimethylsilyl cyclopentadienyl) hafniumdichloride or dimethyl or dihydride, bis(2-n-propyl indenyl) hafniumdichloride or dimethyl, bis(2-n-butyl indenyl) hafnium dichloride ordimethyl, dimethylsilyl bis(n-propyl cyclopentadienyl) hafniumdichloride or dimethyl, dimethylsilyl bis(n-butyl cyclopentadienyl)hafnium dichloride or dimethyl, bis(9-n-propyl fluorenyl) hafniumdichloride or dimethyl bis(9-n-butyl fluorenyl) hafnium dichloride ordimethyl, (9-n propyl fluorenyl)(2-n-propyl indenyl) hafnium dichlorideor dimethyl, bis(1,2-n-propyl, methyl cyclopentadienyl) hafniumdichloride or dimethyl, bis(1,3-n-propylmethylcyclopentadienyl) hafniumdichloride, (n-propyl cyclopentadienyl) (1,3-n-propyl, n-butylcyclopentadienyl) hafnium dichloride or dimethyl and the like.

Typically, the catalyst described above is activated towards olefinpolymerization using one or more activators. As used herein, the term“activator” is defined to be any compound or combination of compounds,supported or unsupported, which can activate a single-site catalystcompound, such as a metallocene, by creating a cationic species from thecatalyst component. Typically, this involves the abstraction of at leastone leaving group from the metal center of the catalyst component.Embodiments of such activators include Lewis acids such as cyclic oroligomeric poly(hydrocarbylaluminum oxides) and so callednon-coordinating activators (“NCA”) (alternately, “ionizing activators”or “stoichiometric activators”), or any other compound that can converta neutral metallocene catalyst component to a metallocene cation that isactive with respect to olefin polymerization.

More particularly, it is within the scope of this invention to use Lewisacids such as alumoxane (e.g., “MAO”), modified alumoxane (e.g.,“TIBAO”), and alkylaluminum compounds as activators, and/or ionizingactivators (neutral or ionic) such as tri(n-butyl)ammoniumtetrakis(pentafluorophenyl)boron and/or a trisperfluorophenyl boronmetalloid precursors. MAO and other aluminum-based activators are wellknown in the art. Ionizing activators are well known in the art and aredescribed by, for example, Eugene You-Xian Chen & Tobin J. Marks,Cocatalysts for Metal-Catalyzed Olefin Polymerization: Activators,Activation Processes, and Structure-Activity Relationships 100(4)CHEMICAL REVIEWS 1391-1434 (2000). The activators may be associated withor bound to a support, either in association with the catalyst component(e.g., metallocene) or separate from the catalyst component, such asdescribed by Gregory G. Hlatky, Heterogeneous Single-Site Catalysts forOlefin Polymerization 100(4) CHEMICAL REVIEWS 1347-1374 (2000).

The aluminum alkyl (“alkylaluminum”) activator may be described by theformula AlR^(§) ₃, wherein R^(§) is selected from the group consistingof C₁ to C₂₀ alkyls, C₁ to C₂₀ alkoxys, halogen (chlorine, fluorine,bromine) C₆ to C₂₀ aryls, C₇ to C₂₅ alkylaryls, and C₇ to C₂₅arylalkyls. Non-limiting examples of aluminum alkyl compounds which maybe utilized as activators for the catalyst precursor compounds for usein the methods of the present invention include trimethylaluminum,triethylaluminum, triisobutylaluminum, tri-n-hexylaluminum,tri-n-octylaluminum and the like.

In general, the activator and catalyst are combined in mole ratios ofactivator to catalyst component from 1000:1 to 0.1:1, and from 300:1 to1:1 in another embodiment, and from 150:1 to 1:1 in yet anotherembodiment, and from 50:1 to 1:1 in yet another embodiment, and from10:1 to 0.5:1 in yet another embodiment, and from 3:1 to 0.3:1 in yetanother embodiment, wherein a desirable range may include anycombination of any upper mole ratio limit with any lower mole ratiolimit described herein. When the activator is a cyclic or oligomericpoly(hydrocarbylaluminum oxide) (e.g., “MAO”), the mole ratio ofactivator to catalyst component ranges from 2:1 to 100,000:1 in oneembodiment, and from 10:1 to 10,000:1 in another embodiment, and from50:1 to 2,000:1 in yet another embodiment. For a more completediscussion of exemplary hafnocence catalysts and activators, pleaserefer to commonly assigned U.S. Pat. Nos. 6,242,545 and 6,248,845.

Polymerization Process

The catalysts described above are suitable for use in any olefinprepolymerization or polymerization process or both. Suitablepolymerization processes include solution, gas phase, slurry phase and ahigh pressure process, or any combination thereof. A desirable processis a gas phase polymerization of one or more one or more olefin monomershaving from 2 to 30 carbon atoms, from 2 to 12 carbon atoms in anotherembodiment, and from 2 to 8 carbon atoms in yet another embodiment.Other monomers useful in the process include ethylenically unsaturatedmonomers, diolefins having 4 to 18 carbon atoms, conjugated ornonconjugated dienes, polyenes, vinyl monomers and cyclic olefins.Non-limiting monomers may also include norbornene, norbornadiene,isobutylene, isoprene, vinylbenzocyclobutane, styrenes, alkylsubstituted styrene, ethylidene norbornene, dicyclopentadiene andcyclopentene.

In a desirable embodiment, a copolymer of ethylene derived units and oneor more monomers or comonomer is produced. The one or more comonomersare preferably an α-olefin having from 4 to 15 carbon atoms in oneembodiment, and from 4 to 12 carbon atoms in another embodiment, andfrom 4 to 8 carbon atoms in yet another embodiment. Preferably, thecomonomer is 1-hexene.

Hydrogen gas is often used in olefin polymerization to control the finalproperties of the polyolefin, such as described in PolypropyleneHandbook 76-78 (Hanser Publishers, 1996). Increasing concentrations(partial pressures) of hydrogen increase the melt flow rate (MFR) and/ormelt index (MI) of the polyolefin generated. The MFR or MI can thus beinfluenced by the hydrogen concentration. The amount of hydrogen in thepolymerization can be expressed as a mole ratio relative to the totalpolymerizable monomer, for example, ethylene, or a blend of ethylene andhexane or propene. The amount of hydrogen used in the polymerizationprocess of the present invention is an amount necessary to achieve thedesired MFR or MI of the final polyolefin resin. In one embodiment, themole ratio of hydrogen to total monomer (H₂:monomer) is in a range offrom greater than 0.0001 in one embodiment, and from greater than 0.0005in another embodiment, and from greater than 0.001 in yet anotherembodiment, and less than 10 in yet another embodiment, and less than 5in yet another embodiment, and less than 3 in yet another embodiment,and less than 0.10 in yet another embodiment, wherein a desirable rangemay comprise any combination of any upper mole ratio limit with anylower mole ratio limit described herein. Expressed another way, theamount of hydrogen in the reactor at any time may range to up to 5000ppm, and up to 4000 ppm in another embodiment, and up to 3000 ppm in yetanother embodiment, and between 50 ppm and 5000 ppm in yet anotherembodiment, and between 100 ppm and 2000 ppm in another embodiment.

Typically in a gas phase polymerization process a continuous cycle isemployed wherein one part of the cycle of a reactor system, a cyclinggas stream, otherwise known as a recycle stream or fluidizing medium, isheated in the reactor by the heat of polymerization. This heat isremoved from the recycle composition in another part of the cycle by acooling system external to the reactor. Generally, in a gas fluidizedbed process for producing polymers, a gaseous stream containing one ormore monomers is continuously cycled through a fluidized bed in thepresence of a catalyst under reactive conditions. The gaseous stream iswithdrawn from the fluidized bed and recycled back into the reactor.Simultaneously, polymer product is withdrawn from the reactor and freshmonomer is added to replace the polymerized monomer.

Further, it is common to use a staged reactor employing two or morereactors in series, wherein one reactor may produce, for example, a highmolecular weight component and another reactor may produce a lowmolecular weight component. In one embodiment of the invention, thepolyolefin is produced using a staged gas phase reactor. This and othercommercial polymerization systems are described in, for example, 2Metallocene-Based Polyolefins 366-378 (John Scheirs & W. Kaminsky, eds.John Wiley & Sons, Ltd. 2000). Gas phase processes contemplated by theinvention include those described in U.S. Pat. No. 5,627,242, U.S. Pat.No. 5,665,818 and U.S. Pat. No. 5,677,375, and European publicationsEP-A-0 794 200 EP-B1-0 649 992, EP-A-0 802 202 and EP-B-634 421.

It has been surprising found that films having a unique balance ofmachine direction (MD) and transverse directions (TD) tear, and/or asimultaneously increasing MD tear with increasing MD shrinkage areproduced when controlling the reactor temperature or ethylene partialpressure or both. Reactor temperature should vary between 60 and 120°C., preferably between 65 and 100° C., more preferably between 70 and90° C., and most preferably between 75 and 80° C. For purposes of thispatent specification and appended claims the terms “polymerizationtemperature” and “reactor temperature” are interchangeable.

The ethylene partial pressure should vary between 80 and 300 psia,preferably between 100 and 280 psia, more preferably between 120 and 260psia, and most preferably between 140 and 240 psia. More importantly, aratio of comonomer to ethylene in the gas phase should vary from 0.0 to0.10, preferably between 0.005 and 0.05, more preferably between 0.007and 0.030, and most preferably between 0.01 and 0.02.

Reactor pressure typically varies from 100 psig (690 kPa) to 500 psig(3448 kPa). In one aspect, the reactor pressure is maintained within therange of from 200 psig (1379 kPa) to 500 psig (3448 kPa). In anotheraspect, the reactor pressure is maintained within the range of from 250psig (1724 kPa) to 400 psig (2759 kPa).

Polymer Products

The inventive polymers typically have a broad composition distributionas measured by Composition Distribution Breadth Index (CDBI) orsolubility distribution breadth index (SDBI). Further details ofdetermining the CDBI or SDBI of a copolymer are known to those skilledin the art. See, for example, PCT Patent Application WO 93/03093,published Feb. 18, 1993. Polymers produced using a catalyst systemdescribed herein have a CDBI less than 50%, more preferably less than40%, and most preferably less than 30%. In one embodiment, the polymershave a CDBI of from 20% to less than 50%. In another embodiment, thepolymers have a CDBI of from 20% to 35%. In yet another embodiment, thepolymers have a CDBI of from 25% to 28%.

Polymers produced using a catalyst system described herein have a SDBIgreater than 15° C., or greater than 16° C., or greater than 17° C., orgreater than 18° C. or greater than 20° C. In one embodiment, thepolymers have a SDBI of from 18° C. to 22° C. In another embodiment, thepolymers have a SDBI of from 18.7° C. to 21.4° C. In another embodiment,the polymers have a SDBI of from 20° C. to 22° C.

In one aspect, the polymers have a density in the range of from 0.86g/cc to 0.97 g/cc, preferably in the range of from 0.90 g/cc to 0.950g/cc, more preferably in the range of from 0.905 g/cc to 0.940 g/cc, andmost preferably in the range of from 0.910 g/cc to 0.930 g/cc. Densityis measured in accordance with ASTM-D-1238.

The polymers have a molecular weight distribution, a weight averagemolecular weight to number average molecular weight (M_(w)/M_(n)) ofgreater than 2.0 to about 5, particularly greater than 2.5 to about 4.5,more preferably greater than about 3.0 to less than about 4.0, and mostpreferably from 3.2 to 3.8.

The polymers have a ratio of z-average molecular weight to weightaverage molecular weight of greater than 2.2 or greater than 2.5 orgreater than 2.8. In one embodiment, this ratio is from about 2.2 and3.0. In another embodiment, this ratio is from about 2.2 to about 2.8.In yet another embodiment, this ratio is from about 2.2 to about 2.5. Instill yet another embodiment, this ratio is from about 2.4 to about 2.8.

The polymers made by the described processes can in certain embodimentshave a melt index (MI) or (I₂) as measured by ASTM-D-1238-E (190/2.16)in the range from 0.1 to 100 dg/min, preferably between 0.2 and 20dg/min, more preferably between 0.3 and 5 dg/min, and most preferablybetween 0.5 and 1.5 dg/min.

In one embodiment, the polymers have a melt index ratio (I₂₁/I₂) (I₂₁ ismeasured by ASTM-D-1238-F) (190/21.6) of from 20 to less than 50. Thepolymers, in a preferred embodiment, have a melt index ratio (I₂₁/I₂) offrom greater than 22, more preferably greater than 25, most preferablygreater that 30.

The polymers may be blended and/or coextruded with any other polymer.Non-limiting examples of other polymers include linear low densitypolyethylenes, elastomers, plastomers, high pressure low densitypolyethylene, high density polyethylenes, polypropylenes and the like.

Compounding, Processing and Articles Therefrom

The polymers produced may also be blended with additives to formcompositions that can then be used in articles of manufacture. Thoseadditives include antioxidants, nucleating agents, acid scavengers,plasticizers, stabilizers, anticorrosion agents, blowing agents, otherultraviolet light absorbers such as chain-breaking antioxidants, etc.,quenchers, antistatic agents, slip agents, pigments, dyes and fillersand cure agents such as peroxide. These and other common additives inthe polyolefin industry may be present in polyolefin compositions from0.01 to 50 wt % in one embodiment, and from 0.1 to 20 wt % in anotherembodiment, and from 1 to 5 wt % in yet another embodiment, wherein adesirable range may comprise any combination of any upper wt % limitwith any lower wt % limit.

In particular, antioxidants and stabilizers such as organic phosphitesand phenolic antioxidants may be present in the polyolefin compositionsfrom 0.001 to 5 wt % in one embodiment, and from 0.01 to 0.8 wt % inanother embodiment, and from 0.02 to 0.5 wt % in yet another embodiment.Non-limiting examples of organic phosphites that are suitable aretris(2,4-di-tert-butylphenyl)phosphite (IRGAFOS 168) and tris(nonylphenyl) phosphite (WESTON 399) Non-limiting examples of phenolicantioxidants include octadecyl 3,5 di-t-butyl-4-hydroxyhydrocinnamate(IRGANOX 1076) and pentaerythrityltetrakis(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (IRGANOX 1010);and 1,3,5-Tri(3,5-di-tert-butyl-4-hydroxybenzyl-isocyanurate (IRGANOX3114).

Fillers may be present from 0.1 to 50 wt % in one embodiment, and from0.1 to 25 wt % of the composition in another embodiment, and from 0.2 to10 wt % in yet another embodiment. Desirable fillers include but notlimited to titanium dioxide, silicon carbide, silica (and other oxidesof silica, precipitated or not), antimony oxide, lead carbonate, zincwhite, lithopone, zircon, corundum, spinel, apatite, Barytes powder,barium sulfate, magnesiter, carbon black, dolomite, calcium carbonate,talc and hydrotalcite compounds of the ions Mg, Ca, or Zn with Al, Cr orFe and CO₃ and/or HPO₄, hydrated or not; quartz powder, hydrochloricmagnesium carbonate, glass fibers, clays, alumina, and other metaloxides and carbonates, metal hydroxides, chrome, phosphorous andbrominated flame retardants, antimony trioxide, silica, silicone, andblends thereof. These fillers may particularly include any other fillersand porous fillers and supports known in the art.

Fatty acid salts may also be present in the polyolefin compositions.Such salts may be present from 0.001 to 2 wt % of the composition in oneembodiment, and from 0.01 to 1 wt % in another embodiment. Examples offatty acid metal salts include lauric acid, stearic acid, succinic acid,stearyl lactic acid, lactic acid, phthalic acid, benzoic acid,hydroxystearic acid, ricinoleic acid, naphthenic acid, oleic acid,palmitic acid, and erucic acid, suitable metals including Li, Na, Mg,Ca, Sr, Ba, Zn, Cd, Al, Sn, Pb and so forth. Desirable fatty acid saltsare selected from magnesium stearate, calcium stearate, sodium stearate,zinc stearate, calcium oleate, zinc oleate, and magnesium oleate.

With respect to the physical process of producing the blend ofpolyolefin and one or more additives, sufficient mixing should takeplace to assure that a uniform blend will be produced prior toconversion into a finished product. The polyolefin can be in anyphysical form when used to blend with the one or more additives. In oneembodiment, reactor granules, defined as the granules of polymer thatare isolated from the polymerization reactor, are used to blend with theadditives. The reactor granules have an average diameter of from 10 μmto 5 mm, and from 50 μm to 10 mm in another embodiment. Alternately, thepolyolefin is in the form of pellets, such as, for example, having anaverage diameter of from 1 mm to 6 mm that are formed from meltextrusion of the reactor granules.

One method of blending the additives with the polyolefin is to contactthe components in a tumbler or other physical blending means, thepolyolefin being in the form of reactor granules. This can then befollowed, if desired, by melt blending in an extruder. Another method ofblending the components is to melt blend the polyolefin pellets with theadditives directly in an extruder, Brabender or any other melt blendingmeans.

The resultant polyolefin resin may be further processed by any suitablemeans such as by calendering, casting, coating, compounding, extrusion,foaming; all forms of molding including compression molding, injectionmolding, blow molding, rotational molding, and transfer molding; filmblowing or casting and all methods of film formation to achieve, forexample, uniaxial or biaxial orientation; thermoforming, as well as bylamination, pultrusion, protrusion, draw reduction, spinbonding, meltspinning, melt blowing, and other forms of fiber and nonwoven fabricformation, and combinations thereof. These and other forms of suitableprocessing techniques are described in, for example, Plastics Processing(Radian Corporation, Noyes Data Corp. 1986).

In the case of injection molding of various articles, simple solid stateblends of the pellets serve equally as well as pelletized melt stateblends of raw polymer granules, of granules with pellets, or of pelletsof the two components since the forming process includes a remelting andmixing of the raw material. In the process of compression molding ofmedical devices, however, little mixing of the melt components occurs,and a pelletized melt blend would be preferred over simple solid stateblends of the constituent pellets and/or granules. Those skilled in theart will be able to determine the appropriate procedure for blending ofthe polymers to balance the need for intimate mixing of the componentingredients with the desire for process economy. Common Theologicalproperties, processing methods and end use applications of metallocenebased polyolefins are discussed in, for example, 2 Metallocene-BasedPolyolefins 400-554 (John Scheirs & W. Kaminsky, eds. John Wiley & Sons,Ltd. 2000).

The polymers produced and blends thereof are useful in such formingoperations as film, sheet, and fiber extrusion and co-extrusion as wellas blow molding, injection molding and rotary molding. Films includeblown or cast films formed by coextrusion or by lamination useful asshrink film, cling film, stretch film, sealing films, oriented films,snack packaging, heavy duty bags, grocery sacks, baked and frozen foodpackaging, medical packaging, industrial liners, membranes, etc. infood-contact and nonfood contact applications. Fibers include meltspinning, solution spinning and melt blown fiber operations for use inwoven or non-woven form to make filters, diaper fabrics, medicalgarments, geotextiles, etc. Extruded articles include medical tubing,wire and cable coatings, pipe, geomembranes, and pond liners. Moldedarticles include single and multi-layered constructions in the form ofbottles, tanks, large hollow articles, rigid food containers and toys,etc.

Other desirable articles that can be made from and/or incorporate thepolymer produced herein include automotive components, sportingequipment, outdoor furniture (e.g., garden furniture) and playgroundequipment, boat and water craft components, and other such articles.More particularly, automotive components include such as bumpers,grills, trim parts, dashboards and instrument panels, exterior door andhood components, spoiler, wind screen, hub caps, mirror housing, bodypanel, protective side molding, and other interior and externalcomponents associated with automobiles, trucks, boats, and othervehicles.

Further useful articles and goods include crates, containers, packagingmaterial, labware, office floor mats, instrumentation sample holders andsample windows; liquid storage containers for medical uses such as bags,pouches, and bottles for storage and IV infusion of blood or solutions;wrapping or containing food preserved by irradiation, other medicaldevices including infusion kits, catheters, and respiratory therapy, aswell as packaging materials for medical devices and food which may beirradiated by gamma or ultraviolet radiation including trays, as well asstored liquid, particularly water, milk, or juice, containers includingunit servings and bulk storage containers.

Film Extrusion and Film Properties

The polymers produced are more easily extruded into film products bycast or blown film processing techniques with lower motor load, higherthroughput and/or reduced head pressure as compared to EXCEED™ resins(available from ExxonMobil Chemical Co.) of comparable melt index,comonomer type and density. Such polyolefin resins have, for acomparable MI, a higher weight average molecular weight and a broaderMWD than does an EXCEED™ resin.

The improvement in tear properties of the film can be expressed as aratio of MD to TD tear (Elmendorf). This ratio will generally be ≧0.9,or ≧1.0, or ≧1.1, or ≧1.2, or ≧1.3. In another embodiment, MD tearvalues of ≧350 g/mil, or ≧400 g/mil, or ≧450 g/mil or ≧500 g/mil arecontemplated. Intrinsic tear, determined by using the same test as bothMD and TD tear, but prepared by compression molding a plaque, isgenerally believed to be greater than MD tear for LLDPE materials.However, the Elmendorf tear divided by intrinsic tear will be ≧1, or≧1.1, or ≧1.2, or ≧1.4, or ≧1.6. In other embodiments, the dart dropimpact resistance (dart) is ≧500 g/mil (±500 g/0.254 mm) as measured byASTM D-1709.

The polymers produced will exhibit a weight average molecular weight offrom 25,000 to 200,000 at corresponding MI (I₂, 190° C./2.16 kg) valuesthat range between 10 and 0.1 dg/mil, and the weight average molecularweight ranges from 80,000 to 150,000 within which range the melt indexrespectively ranges from a value of 3 to 0.5 dg/min. For such polyolefinresins, the melt index ratio (MIR defined by I₂₁/I₂ described herein) is≧20 or ≦40, and ≧25 or ≦38.

The film may have a total thickness ranging from ≧0.1, or ≧0.2, or ≧0.3mils, (≧2.5 or ≧5.1 or ≧7.6 microns) or ≦3 or ≦2.5, or ≦2, or ≦1.5, or≦1, or ≦0.8, or ≦0.75, or ≦0.6 mils (≦76 or ≦64, or ≦51, or ≦38, or ≦25,or ≦20, or ≦19, or ≦15 microns. Typical die gaps range from 30-120 mils,or 60-110 mils. Melt temperatures range from 176° C.-288° C. (350-550°F.), or 198 C-232° C. (390-450° F.). Draw down ratios range from 20-50,or around 30-40.

For a 0.75 mil film for example, tensile strength may vary from 7000 to12000 psi, preferably from 7500 to 12000 psi, more preferably from 8000to 11000 psi, and most preferably from 8500 to 10500 psi; and Elmendorftear in the machine direction may vary from 300 to 1000 g/mil,preferably between 350 and 900 g/mil, more preferably between 400 and800 g/mil and most preferably between 500 and 750 g/mil.

The 1% secant modulus as measured by ASTM D-790 is greater than 10,000psi, greater than 15,000 psi, greater than 20,000 psi, greater than25,000 psi, and greater than 35,000 psi. Preferably, the 1% secantmodulus is greater than 20,000 psi. More preferably, the 1% secantmodulus is greater than 23,000 psi. Most preferably, the 1% secantmodulus is greater than 25,000 psi.

EXAMPLES

In order to provide a better understanding of the foregoing discussion,the following non-limiting examples are offered. Although the examplesmay be directed to specific embodiments, they are not to be viewed aslimiting the invention in any specific respect.

All parts, proportions, and percentages are by weight unless otherwiseindicated. All examples were carried out in dry, oxygen-freeenvironments and solvents. All molecular weights are weight averagemolecular weight unless otherwise noted. Molecular weights (weightaverage molecular weight (M_(w)) and number average molecular weight(M_(n)) and (M_(z)) were measured by Gel Permeation Chromatography(GPC).

Definitions and Testing Periods Melt Index (MI) g/10 min. ASTM D-1238,condition E@ 190° C. Density g/cc ASTM-D-1238 Dart Drop Impact F₅₀ G andg/mil ASTM D-1709 Elmendorf Tear G (g/mil) ASTM-D-1922 Secant Modulus(1%) Psi ASTM D-790A

Melt strength was measured at 190° C. using a commercial instrument(Rheotester 1000) from Goettfert, Germany. CRYSTAF data was obtainedusing a commercial instrument (Model 200) from PolymerChar S.A.,Valencia, Spain. Using a technique outlined in Macromol. Mater. Eng.279, 46-51 (2000). Approximately 30 mg sample was heated to 160° C. at25° C./min in 30 mL of a chlorinated aromatic solvent(ortho-dichlorobenzene or trichlorobenzene) with stirring and held for60 min. The solution was then cooled to 100° C. at 25° C./min andequilibrated for 45 min. The concentration was then monitored as thesample was cooled to 30° C. at 0.2° C./min.

Catalyst Preparation

1. Preparation of Bis(propylcyclopentadienyl)hafnium Dichloride:(PrCp)₂HfCl₂.

HfCl₄ (30.00 g, 93.7 mmol, 1.00 equiv.) was added to ether (400 mL) at−35° C. and stirred to give a white suspension. The suspension wasrecooled to −35° C. and then lithium propylcyclopentadienide (21.38 g,187 mmol, 2.00 equiv.) was added in portions. The reaction turned lightbrown and became thick with suspended solid on adding the lithiumpropylcyclopentadienide. The reaction was allowed to warm slowly to roomtemperature and stirred 17 hours. The brown mixture was filtered to givebrown solid and a straw yellow solution. The solid was washed with ether(3×50 mL) and the combined ether solutions were concentrated to ˜100 mLunder vacuum to give a cold, white suspension. Off-white solid wasisolated by filtration and dried under vacuum. Yield 33.59 g (77%). ¹HNMR (CD₂Cl₂): δ 0.92 (t, 6H, CH₂CH₂CH₃), 1.56 (m, 4H, CH₂CH₂CH₃), 2.60(t, 4H, CH₂CH₂CH₃), 6.10 (m, 4H, Cp-H), 6.21 (m, 4H, Cp-H).

2. Preparation of Bis(propylcyclopentadienyl)hafnium Difluoride:(PrCp)₂HfF₂.

To a murky green-brown solution of bis(propylcyclopentadienyl)hafniumdichloride (70.00 g, 151 mmol, 1.00 equiv.) in dichloromethane (350 mL)was added tributyltin fluoride (98.00 g, 317 mmol, 2.10 equiv.). Thereaction was lighter amber after stirring 10 min. The reaction wasstirred 130 minutes and then filtered through celite to give an ambersolution and off-white solid. The solid was washed with dichloromethaneand the combined dichloromethane solution was evaporated under vacuum,leaving a soupy manila mixture. Pentane (1 L) was added to the mixture,which was stirred 10 minutes and cooled to −35° C. The resultingoff-white solid was filtered and washed with cold pentane (3×75 mL) anddried under vacuum to give a white powder. Yield 56.02 g (86%). ¹HNMR(CD₂Cl₂): δ 0.92 (t, 6H, CH₂CH₂CH₃), 1.55 (m, 4H, CH₂CH₂CH₃), 2.47(t, 4H, CH₂CH₂CH₃), 6.00 (m, 4H, Cp-H), 6.23 (m, 4H, Cp-H). ¹⁹FNMR(CD₂Cl₂): δ 23.9.

Preparation of Active Catalyst

The active catalysts were made at a Al/Hf mole ratio of 120:1 and thehafnium loading on the finished catalyst was 0.685 wt % Hf using thefollowing general procedure. Methylaluminoxane (MAO) 1140 cc of a 30 wt% solution in toluene (obtained from Albemarle Corporation, Baton Rouge,La.) was added to a clean, dry 2 gallon vessel and stirred at 60 rpm and80° F. for 5-15 min. An additional 1500-1800 cc of toluene was addedwhile stirring. The metallocene was dissolved in 250 cc toluene and thetransfer vessel was rinsed with an additional 150 cc of toluene. Themetallocene/MAO mixture was stirred at 120 rpm for 1 hour. Next, 850 gof silica, Ineos 757 (Ineos Silicas Limited, Warrington, England,dehydrated at 600° C.) was added and stirred for 55 min. The catalystwas then dried at 155° F. for 10 hours under flowing nitrogen whilebeing stirred at 30 rpm.

The metallocene for Example 1 was bis(n-propylcyclopentadienyl) hafniumdichloride (21.6 g). The metallocene for Examples 2-6, 12-13 andComparative Example 14 was bis(n-propylcyclopentadienyl) hafniumdifluoride. The catalyst for Example 7 was prepared in a similar mannerexcept that bis(n-propylcyclopentadienyl) hafnium dichloride was usedand the silica was Davison 948 (W.R. Grace, Davison Chemical Division,Baltimore, Md., dehydrated at 600° C.). The metallocene for ComparativeExample 11 was bis(n-propylcyclopentadienyl) hafnium dichloride.

Polymer Production

Using the catalyst systems described above, ethylene/1-hexene copolymerwas produced according to the reaction conditions listed in Table 1.TABLE 1 Reaction Conditions for Examples 1-7, 12 and 13 and ComparativeExamples 11 and 14. Examples 1 2 3 4 5 6 7 11 12 13 14 Production 29 3931 29 36 38 150 58.8 161.1 157.1 136.1 Rate (lb/hr) Hydrogen (ppm) 316306 318 297 303 288 293 398 594 605 572 C₂ partial 240 240 220 220 220220 252 220 252 252 220 pres. (psia) C₆/C₂ ratio 0.0190 0.0196 0.01870.0190 0.0196 0.0194 0.0151 0.0144 0.0168 0.0169 0.0144 Temp. (° C.) 7580 75 75 75 80 77 85 77 77 85 Res. Time (hr) 4.1 2.6 3.9 3.7 2.9 2.8 4.14.2 4.3 4.5 5.0

The ethylene/1-hexene copolymers from Examples 1-6 were produced inaccordance with the following general procedure. Polymerization wasconducted in a 14 inch diameter gas-phase fluidized bed reactoroperating at approximately 350 psig total pressure. The reactor bedweight was approximately 100 pounds. Fluidizing gas was passed throughthe bed at a velocity of approximately 2.0 feet per second. Thefluidizing gas exiting the bed entered a resin disengaging zone locatedat the upper portion of the reactor. The fluidizing gas then entered arecycle loop and passed through a cycle gas compressor and water-cooledheat exchanger. The shell side water temperature was adjusted tomaintain the reaction temperature to the specified value. Ethylene,hydrogen, 1-hexene and nitrogen were fed to the cycle gas loop justupstream of the compressor at quantities sufficient to maintain thedesired gas concentrations. Gas concentrations were measured by anon-line vapor fraction analyzer. The catalyst was fed dry or as amineral oil slurry (17 wt % solids) to the reactor bed through astainless steel injection tube at a rate sufficient to maintain thedesired polymer production rate. Nitrogen gas was used to disperse thecatalyst into the reactor. Product was withdrawn from the reactor inbatch mode into a purging vessel before it was transferred into aproduct drum. Residual catalyst and cocatalyst in the resin wasdeactivated in the product drum with a wet nitrogen purge.

The ethylene/1-hexene copolymers from Examples 7, 12, and 13 andComparative Example 14 were produced in accordance with the followinggeneral procedure. Polymerization was conducted in a 24 inch diametergas-phase fluidized bed reactor operating at approximately 300 psigtotal pressure. The reactor bed weight was approximately 600-700 pounds.Fluidizing gas was passed through the bed at a velocity of approximately2.25 feet per second. The fluidizing gas exiting the bed entered a resindisengaging zone located at the upper portion of the reactor. Thefluidizing gas then entered a recycle loop and passed through awater-cooled heat exchanger and cycle gas compressor. The shell sidewater temperature was adjusted to maintain the reaction temperature tothe specified value. Ethylene, hydrogen, 1-hexene and nitrogen were fedto the cycle gas loop just upstream of the compressor at quantitiessufficient to maintain the desired gas concentrations. Gasconcentrations were measured by an on-line vapor fraction analyzer. Thecatalyst was fed to the reactor bed through a stainless steel injectiontube at a rate sufficient to maintain the desired polymer productionrate. Nitrogen gas was used to disperse the catalyst into the reactor.Product was withdrawn from the reactor in batch mode into a purgingvessel before it was transferred into a product drum. Residual catalystand cocatalyst in the resin was deactivated in the product drum with awet nitrogen purge.

Granular product for Examples 1-7 was screened and dry-blended with 500ppm Irganox® (IR) (available from Ciba-Geigy) 1076, 2000 ppm IR168 and800 ppm Dynamar FX5920A (processing aid from Dyneon) using a double-coneblender. Pelleting of Examples 1 through 6 was carried out on a Werner &Pfleiderer ZSK 57-mm twin-screw extruder equipped with an underwaterpelletizer. Output rate was approximately 175-185 lb/hr and melttemperature was 231° C. (447° F.). Example 7 was pelletized on a Farrelcontinuous mixer at an output rate of 500 lb/h with a specific energyinput of 0.125 hp-hr/lb and a melt temperature of 219° C. Granularproduct for Examples 12-13 and Comparative Example 14 was screened anddry-blended with 1500 ppm IR 1076, 1500 ppn IR 168 and 900 ppm zincoxide. Pelleting was carried out on a Werner & Pfleiderer ZSK 57-mmtwin-screw extruder equipped with an underwater pelletizer. Output ratewas approximately 200 lb/hr and melt temperature was 214-218° C.

Blown Film Production

Blown films were extruded on a 2.5″ Battenfield Gloucester line (30:1L:D) equipped with a 6″ oscillating die. Output rate was 188 lb/hr (10lb/hr/in die circumference) and the die gap was 60 mil. The target filmgauge was 0.75 mil and BUR was held constant at 2.5. FLH was typically19-24″. A standard “hump” temperature profile was used where “BZ” isbarrel zone:BZ1=310/BZ2=410/BZ3=375/BZ4=335/BZ5=335/Adapter=390/Die=390° F.

Cast films were extruded on a 3.5″ Black Clawson line (30:1 L:D)equipped with a 42″ slot die. Line speed was set at 750 ft/min andoutput was adjusted (typically 575-590 lb/h) to achieve a 0.8 mil film.A standard “hump” temperature profile was used where “BZ” is barrelzone: BZ1=350/BZ2=450/BZ3=525/BZ4=540/BZ5=540/BZ6=530/Die=550° F. Thefilm edge was trimmed to give a 20″ roll for testing.

Comparative Example 8 is NTX-095, a commercially available SuperStrength or super hexene Z-N LLDPE from ExxonMobil Chemical Company.Comparative Example 9 is EXCEED® 1018CA, a commercially available mLLDPEfrom ExxonMobil Chemical Company. Comparative Example 10 is Escorene®LL3001.63, a commercially available

Z-N LLDPE from ExxonMobil Chemical Company. Comparative Example 15 isEXCEED® 3518CB, a commercially available mLLDPE from ExxonMobil ChemicalCompany. Comparative Example 16 is EXCEED® 2718CB, a commerciallyavailable mLLDPE from ExxonMobil Chemical Company. Comparative Example17 is Escorene® LL3002.32, a commercially available Z-N LLDPE fromExxonMobil Chemical Company.

Film Properties

The blown film properties and extrusion data are shown in Table II. Castfilm properties and extrusion data are shown in Table III. TABLE IIBlown Film Properties for Examples 1-7: Example 1 2 3 4 5 6 7 MI (I₂)dg/min 0.71 0.96 0.75 0.95 0.87 0.97 0.65 HLMI (I₂₁) dg/min 25.8 23.924.3 29.2 26.7 24.3 18.9 MIR (I₂₁/I₂) 36.3 24.9 32.4 30.7 30.7 25.1 29.1Mw/Mn 3.69 3.24 3.58 3.33 3.68 31.3 2.81 Mz/Mw 2.85 2.59 2.66 2.66 2.712.29 2.38 CDBI (%) 25.5 30.2 23.7 33.5 22.7 32.8 21.7 SDBI (° C.) 21.418.9 20.9 20.8 20.9 18.7 22.0 Melt Strength (cN) 5.8 4.5 5.6 5.2 5.3 4.3˜6.4 Velocity (final/initial) 26 35 26.0 38.0 31 30 Resin Density (g/cc)0.9185 0.9195 0.9164 0.9209 0.9188 0.9176 0.9195 Tensile @ Yield MD 13901400 1320 1480 1390 1300 1440 (psi) Tensile @ Yield TD 1510 1460 13901630 1500 1340 N/a (psi) Tensile @ Break MD 10480 9270 10220 9530 94009780 10400 (psi) Tensile @ Break TD 6400 7090 7180 7160 7490 7510 N/a(psi) Elongation @ Break 290 350 290 330 320 360 300 MD (%) Elongation @Break 610 620 620 650 630 610 N/a TD (%) 1% Secant Modulus 27370 2631024180 28990 26230 22450 30470 MD (psi) 1% Secant Modulus 35110 3192030610 38460 33890 26690 35910 TD (psi) Elmendorf Tear MD 640 550 610 710610 390 760 (g/mil) Elmendorf Tear TD 620 540 540 550 560 510 650(g/mil) MD/TD 1.03 1.02 1.13 1.29 1.09 0.76 1.17 Dart Impact (g/mil) 760620 770 480 680 940 540 Gauge Mic (mils) 0.71 0.72 0.73 0.73 0.74 0.740.73 Shrink MD (%) 79 72 76 74 74 69 77 Shrink TD (%) −27 −20 −24 −21−23 −19 −26 Extrusion Parameters: Melt Temperature (C.) 395 396 395 393396 395 398 Head Pressure (psi) 3710 3570 3780 3410 3550 3590 4110 DiePressure (psi) 2500 2390 2540 2290 2380 2350 2730 Motor Load (amps) 62.465.8 64.1 62.5 63.1 63.6 69.9 Blown Film Properties for ComparativeExamples 8-11. Example 8 9 10 11 MI (I₂) (dg/min) 1.00 0.96 1.01 1.0HLMI (I₂₁) (dg/min) 25.5 15.6 31.3 23.5 MIR (I₂₁/I₂) 25.5 16.3 31.0 23.5Mw/Mn 3.51 2.34 3.91 3.28 Mz/Mw 2.85 1.9 3.25 2.24 CDBI (%) 21.2 64.722.4 40.3 SDBI (° C.) 21.9 11.6 22.0 17.3 Melt Strength (cN) 4.6 3.7 N/aN/a Velocity (final/initial) 36 27 N/a N/a Resin Density (g/cc) 0.92260.9197 0.9174 0.9167 Tensile @ Yield MD 1250 1350 1310 1244 (psi)Tensile @ Yield TD 1310 1390 1400 1265 (psi) Tensile @ Break MD 824010310 9330 7782 (psi) Tensile @ Break TD 5570 6920 6560 9755 (psi)Elongation @ Break 500 440 430 424 MD (%) Elongation @ Break 670 580 760624 TD (%) 1% Secant Modulus 22620 24250 27800 26400 MD (psi) 1% SecantModulus 24780 27650 33680 32100 TD (psi) Elmendorf Tear MD 440 290 420238 (g/mil) Elmendorf Tear TD 760 510 860 495 (g/mil) MD/TD 0.58 0.570.49 0.48 Dart Impact (g/mil) 170 510 190 1238 Gauge Mic (mils) 0.840.73 0.75 1.00 Shrink MD (%) 64 58 70 N/a Shrink TD (%) −15 −12 −21 N/aExtrusion: Melt Temp. (° C.) 430 401 393 N/a Head Pressure (psi) 35503880 3410 3490 Die Pressure (psi) 2260 2490 2290 N/a Motor Load (amps)62.5 71.3 64.4 68.6

TABLE III Cast Film Properties Examples: 12 13 14 15 16 17 MI (I₂)(dg/min) 2.68 3.26 3.78 3.52 2.76 1.87 HLMI (I₂₁) (dg/min) 76.8 97.381.7 58.4 43.9 55.6 MIR (I₂₁/I₂) 28.7 29.8 21.6 16.6 15.9 29.7 Mw/Mn3.21 3.43 3.20 2.45 2.52 4.40 Mz/Mw 2.40 2.46 2.17 1.81 1.74 2.95 CDBI(%) 28.3 28.5 49.9 73.8 70.4 21.3 SDBI (° C.) 20.1 20.1 16.3 12.7 12.722.2 Resin Density (g/cc) 0.9186 0.9201 0.9203 0.9199 0.9201 0.919Tensile @ Yield MD 800 830 780 800 800 860 (psi) Tensile @ Yield TD 730750 710 670 730 830 (psi) Tensile @ Break MD 7670 6980 7190 7690 74307830 (psi) Tensile @ Break TD 5060 4800 4760 5450 5690 4370 (psi)Elongation @ Break 360 370 430 470 450 390 MD (%) Elongation @ Break 730720 680 690 680 850 TD (%) 1% Secant Modulus 15570 16350 16160 1564016610 16480 MD (psi) 1% Secant Modulus 18010 18250 17970 17050 1805019440 TD (psi) Elmendorf Tear MD 390 380 270 210 220 350 (g/mil)Elmendorf Tear TD 520 490 510 490 450 930 (g/mil) MD/TD 0.75 0.78 0.530.43 0.49 0.38 Dart Impact (g/mil) 190 160 160 180 260 100 Gauge Mic(mils) 0.80 0.79 0.76 0.78 0.80 0.81 Extrusion Parameters: MeltTemperature (C.) 553 548 548 562 575 564 Head Pressure (psi) 3500 36703880 4310 4630 4050 Die Pressure (psi) 1060 970 920 1010 1190 1300 MotorLoad (amps) 192 190 193 231 241 205

As shown in the Tables above, lower reactor temperatures surprisinglybroadened the comonomer distribution as evidenced by a decrease in thecomposition distribution breadth index (CDBI) and an increase in thesolubility distribution breadth index (SDBI). Furthermore, lowerpolymerization temperatures or increased ethylene partial pressures orboth surprisingly broadened molecular weight distribution, as evidencedby an increase in Mw/Mn and Mz/Mw. Accordingly, a polyolefin film wasproduced having a high machine direction tear (MD tear), a hightransverse direction tear (TD tear), a high 1% secant modulus, and ahigh dart drop impact resistance (dart).

Unless otherwise indicated, all numbers expressing quantities ofingredients, properties, reaction conditions, and so forth, used in thespecification and claims are to be understood as approximations based onthe desired properties sought to be obtained by the present invention,and the error of measurement, etc., and should at least be construed inlight of the number of reported significant digits and by applyingordinary rounding techniques. Notwithstanding that the numerical rangesand values setting forth the broad scope of the invention areapproximations, the numerical values set forth are reported as preciselyas possible.

All priority documents are herein fully incorporated by reference forall jurisdictions in which such incorporation is permitted. Further, alldocuments cited herein, including testing procedures, are herein fullyincorporated by reference for all jurisdictions in which suchincorporation is permitted.

While the foregoing is directed to embodiments of the present invention,other and further embodiments of the invention may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

1. A method for producing a polyethylene film, comprising: reactingethylene derived units and a comonomer in the presence of ahafnium-based metallocene at a temperature of from 70° C. and 90° C., anethylene partial pressure of from 120 psia and 260 psia, and a comonomerto ethylene ratio of from 0.01 to 0.02 to produce an ethylene basedpolymer; and extruding the ethylene based polymer at conditionssufficient to produce a polyethylene film comprising a 1% secant modulusof greater than 25,000 psi, a dart impact resistance of greater than 500g/mil, and a MD tear strength of greater than 500 g/mil.
 2. The methodof claim 1, wherein extruding comprises blown film extrusion or castfilm extrusion.
 3. The method of claim 1, wherein the comonomer consistsessentially of 1-hexene.
 4. The film of claim 1, wherein thehafnium-based metallocene is represented by the following formula:Cp^(A)Cp^(B)HfX₂ wherein each X is independently selected from the groupconsisting of fluorine, chlorine, iodine, bromine, and combinationsthereof; and Cp^(A) and Cp^(B) are independently selected from the fromthe group consisting of cyclopentadienyl, indenyl, tetrahydroindenyl,fluorenyl, and a combination thereof.
 5. The film of claim 1, whereinthe hafnium-based metallocene is represented by the following formula:Cp^(A)(A)Cp^(B)HfX_(n) wherein each X is independently selected from thegroup consisting of fluorine, chlorine, iodine, bromine, andcombinations thereof; Cp^(A) and Cp^(B) are independently selected fromthe from the group consisting of cyclopentadienyl, indenyl,tetrahydroindenyl, fluorenyl, and a combination thereof; A is a divalenthydrocarbon group comprising at least one atom selected from the groupconsisting of carbon, oxygen, nitrogen, silicon, aluminum, boron,germanium, tin and combinations thereof; and n is an integer from 0 to4.
 6. The film of claim 1, wherein the hafnium-based metallocenecomprises two symmetrically substituted cyclopentadienyl groups and adihalide bonded to a hafnium atom.
 7. The film of claim 1, wherein thehafnium-based metallocene is bis(propylcyclopentadienyl) hafniumdichloride.
 8. The film of claim 1, wherein the hafnium-basedmetallocene is bis(propylcyclopentadienyl) hafnium difluoride.
 9. Thefilm of claim 1, wherein the temperature is from 75° C. to 80° C. 10.The film of claim 2, wherein the ethylene partial pressure is from 220psia to 260 psia.
 11. The film of claim 3, wherein the temperature isfrom 75° C. to 80° C. and the ethylene partial pressure is from 220 psiato 260 psia.
 12. The film of claim 4, wherein the polymer is aco-polymer consisting essentially of 1-hexene and ethylene derivedunits.
 13. The film of claim 12, wherein the polymer has a 1-hexene toethylene molar ratio 0.0150 to 0.02.
 14. The film of claim 1, whereinthe polymer has a Composition Distribution Breadth Index (CDBI) of from20% to 50% and a Solubility Distribution Breadth Index (SDBI) of from18° C. to 22° C.
 15. The film of claim 1, wherein the polymer has aComposition Distribution Breadth Index (CDBI) of from 20% to 35% and aSolubility Distribution Breadth Index (SDBI) of from 18.7° C. to 21.4°C.
 16. The film of claim 1, wherein the polymer has a ratio of Z-averagemolecular weight to weight average molecular weight of from 2.2 to 3.17. The film of claim 1, wherein the polymer has a ratio of Z-averagemolecular weight to weight average molecular weight of from 2.2 to 2.8.18. The film of claim 1, wherein the polymer has a ratio of Z-averagemolecular weight to weight average molecular weight of from 2.4 to 2.8.19. The film of claim 1, wherein the polymer has a CompositionDistribution Breadth Index (CDBI) of from 20% to 50%, a SolubilityDistribution Breadth Index (SDBI) of from 18° C. to 22° C., and a ratioof Z-average molecular weight to weight average molecular weight of from2.2 to 3.